Saturn facts and information

An overview of the planet Saturn including statistics, moons, and planetary comparisons.

Photo Credit: Christoph Ermel

By Melissa Mayntz
Saturn is one of the most recognizable and beautiful objects in the solar system. At the same time, however, this ringed giant has many secrets astronomers have struggled to uncover for centuries.

The Sixth Planet

Named for the Roman god Saturnas, the god of farming and father of Zeus, Saturn was first observed through a telescope in 1610 by Galileo Galilei. From his preliminary observations to today's spectrometers and sensory probes, we have learned much about this unusual planet in four hundred years.

The sixth planet from the Sun, Saturn is the second-largest in the solar system, outclassed only by Jupiter. It is a gas giant, composed of ninety-three percent hydrogen, six percent helium, and trace amounts of other gases that contribute to its striped appearance. The abundance of hydrogen makes the planet appear a yellowish butterscotch color, slightly darker at the poles.

Saturn has four principle layers. The core is solid rock, roughly Earth-size, followed by a layer of liquid metallic hydrogen. Further away from the core, the metallic hydrogen becomes liquid molecular hydrogen, and the topmost layer is gaseous. As a gas giant, Saturn has no distinct surface, but great ice and ammonia clouds form distinct atmospheric bands and stripes. The planet's rotation creates high winds, up to 1,100 miles (1,800 kilometers) per hour at the equator, and as Saturn reaches the end of its summer when the atmosphere is warmest, an immense storm appears. It was first observed in 1876, and has been christened the Great White Spot because of its visibility and brilliance. It recurs approximately every thirty years.

Saturn rotates on its axis once every ten hours and fourteen minutes, but its revolution around the Sun is far slower: a year on Saturn is equivalent to 29.5 years on Earth. With an average distance from the Sun of 888 million miles, Saturn moves approximately six miles (9.64 kilometers) per second.

With such a swift rotation, Saturn bulges slightly at the equator and appears slightly flattened. It is 74,900 miles (120,500 kilometers) in diameter, roughly 9.45 times the size of the Earth. Because it is composed of gases, however, Saturn is the least dense planet in the solar system, and its gravity is only slightly higher than Earth's.

Saturn's thermodynamic characteristics have puzzled scientists for years. Unlike other planets, Saturn actually gives off more heat than it absorbs from the Sun. Its core temperature is 21,700 degrees Fahrenheit (12,000 degrees Celsius), and the surface temperature averages -215 degrees Fahrenheit (-139 degrees Celsius). Scientists speculate that Saturn's atmosphere traps and intensifies absorbed radiation while friction from its liquid metallic layer simultaneously generates additional heat. As more sophisticated equipment is used to observe the planet, scientists will test and refine these theories.

Like Earth, Saturn has a magnetic field, but it is nearly one thousand times more intense. The poles are inverted on Saturn, which would force a compass to point south rather north. The intense magnetic radiation creates stunning auroras near the planet's poles, similar to Earth's aurora borealis.

Saturn's Family

Saturn's most stunning feature is its distinct rings. First observed by Galileo, who thought the planet had mysterious ears or handles, and later defined by Dutch astronomer Christiaan Huygens' observations in 1655, we now know that Saturn has seven distinct rings, three of which can be easily seen with a backyard telescope. The rings are composed of ice and rock chunks ranging in size from dust particles to house-size boulders. Each ring is contains thousands of tiny ringlets, all orbiting Saturn parallel to the equator, where the gravity is strongest and keeps the particles aligned. The rings are over 225,000 miles wide - the distance from the Earth to the Moon - but only a few hundred feet thick. Because of their thinness, as Saturn revolves around the Sun and its position relative to the Earth changes, the rings appear to move and eventually disappear. In 2002, the rings were at their widest, and by 2009 they will virtually vanish.

Scientists have several theories about the origin of Saturn's rings. The particles may be leftover from the planet's formation but the gravitational forces are not strong enough to pull them into the planet itself. Denser rings may be remnants of an ancient moon that was destroyed by an asteroid or meteor.

Saturn is orbited by more than just rings: there are thirty-one known moons ranging from 83,000 to eight million miles from the planet. The largest and most famous moon is Titan, the second largest moon in the solar system (only Ganymede, a moon of Jupiter, is larger). Titan is the only moon with a significant atmosphere, composed mainly of nitrogen and small amounts of methane.

In addition to Titan, seventeen of Saturn's other moons have been named, all of them after Greek gods and goddesses such as Phoebe, Rhea, Helene, Calypso, and Mimas. Moons are named once astronomers have verified their orbits and determined that they are indeed natural satellites rather than captured debris such as wandering asteroids or comets. Different moons have different compositions, including ice, rock, and soot, which affect their ability to reflect sunlight. Saturn's moons vary in their brightness because of their different compositions.

Saturn's Neighbors

Saturn shares several distinct characteristics with its planetary neighbors. Jupiter, Uranus, and Neptune are also gas giants that lack a solid surface. They all have rings, but none are as dense and brilliant as Saturn's and they are only visible through the most powerful telescopes. All three of Saturn's nearby neighbors have multiple moons, but only Jupiter has a greater number of natural satellites. Jupiter's Great Red Spot is a tremendous storm similar to Saturn's Great White Spot, but it is far more powerful and is a continual presence in the planet's atmosphere.

Despite all we have learned about Saturn in the past four centuries, the gas giant still hides many secrets from our probes, satellites, and telescopes. As more sophisticated equipment is developed and eventually poised to rendezvous with this mysterious planet, scientists will continue to uncover facts and information that gradually reveal its true nature and role in the solar system.